1. Field of the Invention
The present invention generally relates to ink jet heads and, more specifically, to an ink jet head which has been improved to enable reliable connection of an external electrode and an electrode connecting portion by wire bonding or the like. The invention also relates to a method of manufacturing such an ink jet head.
2. Description of the Background Art
In recent years, a non impact printer such as an ink jet type printer which is adapted to provide colorization and higher gray scale level is rapidly diffused taking the place of an impact printer. Among such printers, a drop on demand type printer which ejects only a required amount of ink for printing has received a great deal of attention because of its high printing efficiency, low cost and low running cost and the like. A Kaiser type printer using a piezoelectric element or a thermal jet type printer is primarily used.
However, a Kaiser type printer is not readily reduced in size and thus unsuitable for greater integration. A thermal jet type printer is suitable for greater integration, but must meet strict requirements for long-lasting ink since it utilizes for ejection the energy of bubbles produced in the ink by a heater. In addition, in the thermal jet type printer, the heater life is limited and power consumption is considerable.
To solve the above mentioned problems, an ink jet type printer utilizing a shear mode of a piezoelectric material has been proposed. In this printer, an electric field is applied in the direction orthogonal to the polarizing direction of the piezoelectric material with use of an electrode formed on an ink channel wall of the piezoelectric material to deform the channel wall in the shear mode, so that ink droplets are ejected by pressure vibration caused at the time. As such, the ink jet type printer is adapted to provide higher density of nozzles, lower power consumption, and higher driving frequency. The structure of such an ink jet head utilizing the shear mode will be described with reference to FIG. 20.
Referring to FIG. 20, the ink jet head includes a base member 1 having a plurality of grooves 4 formed in a piezoelectric material which has been subjected to a polarization process in the vertical direction, a cover member 2 including an ink supply port 21 and a common ink chamber 22, and a nozzle plate 9 having nozzles 10, which members are bonded together to define ink channels 4. On the upper half portion of the channel wall 3, an electrode 5 is formed for application of an electric field. The rear end portion of the ink channel is formed in an R shape corresponding to a diameter of a dicing blade used for groove formation. The portion denoted by 6 has a shallow groove as an electrode connecting portion which is also formed by the dicing blade for connection with respect to an external portion. The electrode formed in shallow groove portion 6 is connected to an external electrode 8 such as a flexible printed circuit board at the rear end portion of shallow groove portion 6 by a bonding wire 7.
Now, a manufacturing method of the ink jet head shown in FIG. 20 will be described with reference to FIG. 21 and 22.
As shown in FIG. 21, a dry resist film 11 allowing a dicing process is laminated on a piezoelectric material 12 which has been vertically subjected to a polarization process.
Then, as shown in FIG. 22, a groove to be ink channel 4 as well as, shallow groove portion 6 (slope) are formed by the dicing blade. Thereafter, diagonal vapor deposition is performed in the A and B directions in FIG. 22, with the incident direction set in such a way that a metal to be an electrode adheres only to the upper half portion of channel wall 3. Then, dry resist film 11 is lifted off to provide a base material 1 as an actuator having a metal film 5 formed on the upper half portion of channel wall 3 and in shallow groove portion 6 as shown in FIG. 20.
Returning to FIG. 20, cover member 2 has ink supply port 21 and common ink chamber 22 which are formed by machining or sand blasting. If the sand blasting is employed, it may be performed after masking the portion excluding ink supply port 21 and common ink chamber 22 with a resist film or a metal mask.
If nozzle plate 9 is formed of a polymeric material, nozzles, each having a prescribed size, are formed by an excimer laser process Alternatively, nozzles may be formed in a metal material by punching or the like. Thus manufactured base member 1, cover member 2 and nozzle plate 9 are bonded together by an adhesive in a desired positional relationship.
Thus manufactured ink jet head has ink supply port 21 connected to an external ink storage tank (not shown) and common ink chamber 22 through which ink is supplied to the plurality of ink channels 4. The electrode formed on the upper half portion of channel wall 3 is connected at the R-shape portion of the ink channel rear end portion to provide the same potential in respective ink channel 4 and connected to external electrode 8 through shallow groove portion 6. The electrodes formed at respective ink channels 4 are individually connected to external electrode 8.
A voltage is applied by external electrode 8 such that a prescribed ink channel is selected in accordance with printing data and an electric field is applied in the direction orthogonal to the polarizing direction of channel wall 3. Channel wall 3 supplied with the voltage is subjected to shear deformation. As a result, pressure wave is caused in the ink channel to eject ink droplets from nozzle 10. Note that although in FIG. 20 the electrode connecting portion and the external electrode are connected by bonding wire 7, the connection may be made with use of an anisotropic conductive film (ACF) as is conventionally known.
A conventional ink jet head uses a metal film formed in shallow groove portion 6 as the electrode connecting portion. Thus, the metal film is positioned in the shallow groove. Further, the metal film is formed when forming the metal film to be the electrode on the upper half portion of channel wall 3. Thus, there is dry resist film 11 to be a mask at the portion excluding the shallow groove. As a result, a metal film of a sufficient thickness cannot be formed at the bottom of shallow groove portion 6 because of shadowing with diagonal vapor deposition.
The aforementioned problems are discussed in the following.
FIG. 23 is a cross sectional view of shallow groove portion 6 shown in conjunction with formation of the metal film. Assume that the width of the channel formed in base member 1, the depth of the channel, and the thickness of dry resist film 11 are respectively 81 xcexcm, 300 xcexcm, and 30 xcexcm. Then, the incident angle for diagonal vapor deposition would be about 24xc2x0 with respect to the normal line when forming the metal film on the upper half portion of the channel wall. In this case, diagonal vapor deposition would be performed on shallow groove portion 6 of FIG. 20 with the same incident angle as shown in FIG. 23. FIG. 24 is a photograph showing a cross section of the metal film formed on the shallow groove portion when the depth of the shallow groove portion, the thickness of the dry resist film, and the incident angle for diagonal vapor deposition with respect to the normal line are respectively 25 xcexcm, 30 xcexcm, and 24xc2x0. Note that FIG. 24 shows the metal film after the dry resist film is lifted off.
Referring to FIG. 24, with the depth of the shallow groove portion of 25 xcexcm, in the middle of the shallow groove bottom, the metal film is formed to have a step in the region with a width of about 32 xcexcm. Thus, in wire bonding, bonding must be made in the middle of the step. The positioning failure of the bonding wire with respect to the step causes falling or inclining of the wire, and therefore accurate positioning must be ensured.
The height electrode portion is smaller than that of base member 1. The smaller depth of the shallow groove portion provides the greater width of the metal film formed at the bottom of the groove portion. However, a depth of at least 10 xcexcm is required for the shallow groove portion, taking into account machining accuracy and R of the edge portion of the dicing blade. This will be described in detail with reference to FIGS. 25A and 25B showing cross sections of the dicing blade. When dicing blade 30 is unused, it has a right-angled corner E as shown in FIG. 25A. As dicing blade 30 is used, it comes to have a rounded corner as shown in FIG. 25B. If use of dicing blade 30 as shown in FIG. 25B usually provides a shallow groove having a depth of 10 xcexcm, actually, the dry resist film cannot be cut to have a width of no more than 60 xcexcm. As a result, the width of the metal film in the shallow groove portion becomes smaller.
On the other hand, the use of the dicing blade as shown in FIG. 25A provides a shallow groove having an infinitely small depth. However, this leads to a higher production cost. Thus, the depth of the shallow groove portion must be at least 10 xcexcm.
If the electrode of the electrode connecting portion is formed at the bottom of the shallow groove portion, bonding failure may occur when making a connection with respect to the external electrode by wire bonding. This will be discussed in detail with reference to FIG. 26 which shows a cross section of capillary 40 and bonding wire 50 used for wire bonding.
Referring to FIG. 26, capillary 40 has a concave shape facing downward to surround bonding wire 50 between both ends 41 of the capillary when viewed in section. The bonding wire generally has a diameter of about xcfx8650 xcexcm and capillary 40 has a width of about 100 xcexcm. When wire bonding is performed with capillary 40 having the shape as shown in FIG. 26, the end (portion denoted by B) of the capillary is brought into contact with a convex portion (portion denoted by A) of base member on either side of shallow groove portion 6. As a result, ultrasonic energy for bonding would not be transferred to the wire efficiently. Thus, the bonding wire is not fully welded, deteriorating bonding of the wire and the metal film at the shallow groove portion. If the connection of the electrode connecting portion and the external electrode is made with use of an anisotropic conductive film (ACF), the presence of metal film in the concave portion of the electrode connecting portion results in connection failure.
Electrode surface can be made higher than the base member by increasing the thickness of the metal film of the electrode at the electrode connecting portion. However, as stated previously, since the depth of shallow groove portion 6 must be at least 10 xcexcm, the metal film of at least 10 xcexcm is required. This leads to a problem associated with production cost and time. Another conventional method of manufacturing an ink jet head involves formation of grooves in piezoelectric substrate 10 without using any dry resist film as shown in FIG. 20. In this method, the metal film formed on top of the upper portion of channel wall 3 and the metal film at the electrode connecting portion are individually removed by machining after the metal film is formed. In this case, although a convex portion can be formed on the electrode surface of electrode connecting portion 23, machining of the upper portion of the channel wall may destroy a channel wall, possibly reducing yield. Further, it is difficult to provide channel walls of the same height. In bonding cover member 2, it is not tightly bonded to the upper portion of channel wall 3, whereby ink leaks out from one channel to another.
As described above, the conventional ink jet head having the electrode of the electrode connecting portion at the bottom of the shallow groove portion suffers from the problem that connection failure occurs when making a connection to the external electrode by wire bonding or with use of an ACF. In addition, if the shallow groove at the electrode connecting portion is made to have a smaller depth, a dicing blade with a right-angled corner must be used, resulting in greater production cost.
Moreover, if the metal film on the upper portion of the channel wall is removed by machining and the electrode connecting portion is provided at the convex portion, destruction of the channel wall may occur leading to smaller yield. In addition, the variation in channel wall height causes ink to leak out from one channel to another.
The present invention is made to solve the aforementioned problems. An object of the present invention is to provide an ink jet head which has been improved to enable reliable connection of an external electrode without increasing production cost.
Another object of the present invention is to provide a manufacturing method of such an ink jet head.
The ink jet head according to one aspect of the present invention is provided with a base member which is at least partially formed of a piezoelectric material, which includes a plurality of first grooves formed in its surface, separated from one another by walls, and arranged in parallel, and which further includes electrodes respectively formed on parts of the walls of the first grooves. A cover member defining ink channels to be pressure chambers is provided on the base member to cover the plurality of first grooves. Nozzles communicate with the ink channels. A plurality of electrode connecting portions are provided in the surface of the base member electrically connected to the electrode for external connection. The ink jet head applies a driving voltage to the electrode to cause shear deformation of the wall, thereby causing pressure vibration to the ink channel to eject ink from the nozzles. The plurality of electrode connecting portions are electrically isolated from one another by the second grooves formed in the surface of the base member. The surface of the electrode connecting portion is substantially flush with the upper surface of the wall.
In this structure, since a metal film forming the electrode of the electrode connecting portion is substantially made flush with the upper surface of the wall in connecting the electrode connecting portion, used for supplying a voltage to a piezoelectric material of the ink jet head, to the external electrode, so that a reliable connection is made without causing connection failure by wire bonding or with use of an ACF.
In a preferred embodiment of the present invention, the end portion of the first groove on the side free from nozzles has a slope, on which the electrode connecting portion extends. The electrode and the electrode connecting portion are in electrical communication with each other through the extending portion.
In this structure, the electrode on the channel wall is individually connected to the metal film formed on the slope. In addition, the slope reduces the effect of shadowing during metal film formation, so that the metal film can be formed on the slope with a sufficient thickness. Since the electrode on the channel wall forming the ink channel is connected to the electrode connecting portion through the metal film on the slope, the electrodes formed on the channel walls are not subjected to short circuit, and a reliable connection is made without causing connection failure.
In a more preferred embodiment of the present invention, the sloped portion partially has a flat surface in the direction toward the nozzles, and a distance of the flat surface from the surface of the base member is at most 100 xcexcm.
In this structure, when forming the metal film, the effect of shadowing is reduced and the metal film to be the electrode is formed at the bottom of the slope, whereby a reliable electrical connection of the electrode connecting portion and the electrode formed on the channel wall is ensured.
In a more preferred embodiment of the present invention, each electrode connecting portion extends in the direction away from the nozzles starting from the slope.
In this structure, the region separating the electrode connecting portions is in the region of the slope, so that the electrodes formed on the channel walls are isolated to prevent short circuit while being connected to the electrode connecting portions. When grooves are formed for isolating the electrode connecting portions, the groove portions do not reach the channel wall regions. Thus, the strength of the channel wall is not reduced.
In a more preferred embodiment of the present invention, the electrode connecting portion at the slope portion has a length of at least 50 xcexcm.
In this structure, a region separating the electrode connecting portions is in the region of the slope while being electrically connected to the electrode on the channel wall over a distance of at least 50 xcexcm. Thus, the electrodes on the channel walls are reliably isolated to prevent short circuit while being connected to the electrode connecting portions.
In a more preferred embodiment of the present invention, the electrode connecting portion has a width of at least 40 xcexcm and at most 100 xcexcm.
In this structure, since the electrode connecting portion for connection to the external electrode has a width of at least 40 xcexcm and at most 100 xcexcm, a reliable electrical connection can be made by wire bonding or with use of an ACF.
A method according to the second aspect of the present invention refers to a method of manufacturing an ink jet head including: a base member at least partially formed of a piezoelectric material, including a plurality of first grooves formed in its surface, separated by walls and arranged in parallel, and including an electrode on parts of the walls of the first grooves; a cover member formed to cover the plurality of grooves of the base member to provide ink channels of a pressure chamber; and nozzles provided in communication with the ink channel, where a driving voltage is applied to the electrode to cause shear deformation of the wall and pressure vibration to the ink channel to allow ink to eject from the nozzles. First of all, a substrate at least partially formed of the piezoelectric material is prepared. Grooves are formed in the surface of the substrate with use of a resist having a prescribed pattern, so as to form an ink channel of the first groove having one end portion, on the side opposite the nozzles, formed with a slope. A metal film is formed on the slope and the substrate excluding the bottom portion of the ink channel. The metal film is divided into a plurality of portions, so that a plurality of electrically isolated electrode connecting portions are formed.
In this structure, the metal film can be formed with the electrode connecting portion to be connected to the external electrode not covered with a polymeric material by means of wire bonding or with use of an ACF. Thus, the unwanted effect of shadowing is not produced in forming the metal film, so that the metal film with a sufficient thickness can be provided. Further, after the metal film is formed, the electrode connecting portions are isolated. Thus, a convex portion is readily provided at the electrode portion of the electrode connecting portion, whereby a reliable connection is made in connecting the external electrode by wire bonding or with use of an ACF.
In a preferred embodiment of the present invention, a boundary of the region covered with the resist and that not covered with the resist is a region of the slope.
In this structure, since the boundary of the regions covered and not covered with the polymeric material is in the region of the slope, unwanted shadowing is not caused to the region not covered with the polymeric material in the region of the slope, when forming the metal film. Thus, the metal film can be formed with a sufficient thickness and an electrical connection of the electrode on the channel wall and the electrode connecting portion is ensured.
In a more preferred embodiment of the present invention, the isolation of the electrode connecting portions involves physical removal of portions of the metal film and the base member and formation of the second grooves.
In this structure, after the metal film is formed on the base material, grooves for isolating the electrode connecting portions are formed. Thus, the electrode surface of the electrode connecting portion can be readily provided with a convex portion and a reliable isolation of the electrodes of the electrode connecting portions is enabled since the grooves are physically formed.
In a more preferred embodiment of the present invention, the second groove for isolating the electrode connecting portions extends to the upper surface of the wall.
In this structure, the grooves for isolating the electrode connecting portions are also positioned in the region covered with the polymeric material, so that the electrodes on the channel walls preliminary isolated by the polymeric material, the electrodes on the slopes that are connected separately from the electrodes on the channel walls, and the electrode connecting portions connected to the external electrode are respectively connected together. Thus, the electrodes on the channel walls are reliably connected to the external electrode without causing short circuit.
The foregoing and other objects, features, aspects and advantages of the present invention will become more apparent from the following detailed description of the present invention when taken in conjunction with the accompanying drawings.